A developing device of an image forming apparatus stirs a developer containing a toner and a carrier, thereby triboelectrically charging the toner. The charged toner is adsorbed on a magnet roller and thereafter transferred to a photoconductive drum.
In this manner, the developing device causes the toner contained in the developer to adhere to the photoconductive drum according to an electrostatic latent image. When the toner is consumed by development, the toner is supplied to the developing device. The developing device includes a stirring screw. The stirring screw stirs the developer and the suppled toner, and also circulates and conveys the developer in the developing device.
However, the suppled toner does not mix into the existing developer and is conveyed along the surface on the developer in some cases. In such a case, mere stirring of the toner is insufficient.
The toner which is insufficiently stirred is not sufficiently charged, and image formation is hardly accomplished.